In order to investigate the strength characteristics of lateritic clay in a wide range of suction

a series of constant water content direct shear tests is carried out on the unsaturated Guilin lateritic clay. With regard to the suction applied

the suctions can be imposed by using the pressure plate method and vapor equilibrium method. The effect of soil density on soil-water characteristic curve can be ignored

and thus the test under constant water content is that at constant suction. The test results show that with the increase of suction

unsaturated shear strength and total cohesion increase first and then decrease

and reach a maximum values at suction of 7 MPa. The internal friction angle does not change significantly when the suction is higher than 7 MPa

indicating that the suction contributes to the shear strength by changing the cohesion in a high range of suction. When suction is higher than 70 MPa

shear strength varies slightly with increase of suction. Finally

by using results of mercury intrusion porosimetry tests

strength characteristics of Guilin lateritic clay in a wide range of suction are explained from the perspective of pore-size distribution.